Sound recorder



Dec. 16, 1930.' c. F. WIEBUSCH SOUND RECORDER Filed Aug. 25, 1928 w TEMPEPA TUPE IN F HY 5 M am I P W., l. m. 0/ Y B v Patented Dec. 16, 1930 UNITED STATES- PATENT orrlcr.

CHARLES E. wrEnuscn, on NEW YORK, N. 2., assreuon T BELL TELEPHONE LABORA- TORIES, mcoaronmrnn, or NEW YORK, N, Y., .A. CORPORATION oE-NEw Yonx SOUND RECQRDEB Application filed August 25, 1928. Serial No. 302,083.

This inventionrelates to vibration damping devices and more particularly to an arrangement for maintaining the damping action at a constant value in electro-magnetic devices such as sound recorders;

I In Patent No. 1,663,884 to Harrison, March 29, 1928, there is disclosed a translating device in which the moving system has attached to it a mechanical terminating impedance consisting of a rubber line of high dissipative properties whereby substantially constant response isobtained over a wide range of ire quencies As an a ternative device for this purpose it has been proposed to use an oil damping unit'which consists of a wing-like member attached to the moving system of thedevice and adapted-to vibrate in a viscous medium between two adjustable plates. In units of this sort the mechanical resistance or damping action of the Wing member 1s proportional to the viscosity of the damplng medium employed. The response of such a dc vice therefore will vary with the temperature so that for high quality work calibration must be made at approximately the temperature at which the unit is to be used.

It is the object of the present invention to overcome this objection and to provide a damping unit which offers substantially con-.

stant resistance to motion over a wide range of both frequency and temperature.

According to the preferred embodiment of this invention variations in damping effect due to changes of viscosity of the damping medium with temperature are prevented automatically by the movement of the ad ust-' able plates in accordance'with the expansion and contraction of oil or other fluid means in secondary chambers on the other side of the plates. One or both of the plates may be regulated in this way according to the degree of accuracy required.

In the drawing, Fig. 1 is an assembly view showing .;how the present invention may be used with an oil-damped recording dev1ce.-

Fig. 2 is a sectional view of the temperature compensating uniti- Figs. 3 and 4 are-sectional views through the damping chamber as indicated, and

Fig. 5 shows a series of curves by means of which the design of the device is facilitated.

Referring now to 1, the recorder shown is of thebalanced armature type and, with respect to the arrangement of the parts for translating electrical variations in the windings 2425 into mechanical vibrations of the recording stylus 30, is essentially the same as that disclosed in the above Harrison patent. The recording stylus 30 is carried by a stylus holder 29, the horizontal, section 28 of which serves also as a supporting membar for the armature 17. When the record 32 is being cut, an oscillatory motion is imparted to the armature by the interaction of the currents corresponding to the sounds to'be recorded and the magnetic field of the recorder as fully described in the Harrison patent so that the stylus holder will vibrate about its horizontal axis.

It will be evident that in the present invention the damping unit 2 replaces the rubber line of the patent and that the wing'member 33 engages threads on the end of member 28 and is held in proper adjustment by lock nut 34. As the member 28 oscillates in accordance with the currents in coils 2425 the wing member 33 undergoes a similar oscillatory motion and displaces the oil in the gaps 8 and 35, thereby introducing the required damping action. The foregoing detailed explanation deals entirely with the devices of the prior art but it is a necessary prerequisite to a proper understanding of the recorder damping gap 8 and the chamber 5 and yet flexes sufficiently to permit the'piston to vary the gap in accordance with temperature changes. The casing is recessed at 9 to receive the end of piston rod 10 as indicated, and thereby maintain the piston in proper alignment. The casing is made oiltight by soldering around the periphery of the diaphragm and'sealing jofl' openin s 11 and 12 after the unit has been filled wit oil.

The exact'sizeof the oil chamber necessary to maintain constant damping depends,; of course,-upon the viscosity of the oil, the ratio of the temperature coeflicients of the oil and the casing material, the dimensions of the gap, the effective area of the diaphragm and whether one .or two compensating units are used. Inthe present instance brass is used I as a casing material, the gaps of the damping unit are about 15.mils each and the effective area A of the diaphragm is taken as .10 square inches. An oil which, has. been found satisfactory forthe purposes of this invention is a mixture of 74% polymerized linseed oil and 26% kerosene.

These factors having been determined, the

required volume of the compensating chamher is fixed by the distance the piston must' move per degree rise in temperature to maintain the damping within permissible limits of variation. In order to obtain theoretically a first approximation of this movement,

curves of a'X the viscosity of the oil, and 1 were plotted as shown in Fig. 5. Values of X were obtained from the equation X 9(% 0 G being the oil gap at the temperature t and 9 being the assumed expanslon per degree rise in temperature (in this case An indication of'the variations in mechan ical resistance or -damping with temperature.

is obtained by plotti resents the product The flatter curve R I ing g arbitrarily to the value a curve R which repthe first two curves.-

9 5 .104 mile per degree F. The apparent coeficientyof e d of the oil used, abrass easing is ut 35 X 10" Since varlations up to 1.0% do not afiect the to for temperature variations from per degree F. The necessary movement of the piston per degree F. due to the expansion of theoil in chamber 5 is then represented by ic'rom which the required volume of the compensating chamber 35 x 10.- Since the tenfperature range of a studio is generally rathersmall, one variable gap will provide sufficient temperature compensation in many cases. Experiments along this line indicate that one unit may be designed to .03( cubic inches.

give satisfactory regulation over arange of about 2/3 that possible when both gaps are made variable.

Whilethis invention has been described with reference to a particular embodiment, it is intended to be limited only by the following claims.

What is claimed is:

1. In a vibration, damping device the method of preventing variations in the damping action which consists in. varying the size of the damping chamber in accordance with the volume variations of fluid external to the damping chamber.

2. In a vibration containing viscous matter, a damping member moving in said matter and fluid means r espons'ive to temperature changes for preventing variations 1n the efi'ectiveness of said damping device. I

3...*In ;-a mechanical vibration damping device, a casing, a pair of spaced'iplates, a member adapted to oscillate between the plates, viscous matterin said casing-"to impede the oscillations ofsaid member and means respon sive to temperature changes for varying the spacing of said plates.

I 4. In a mechanical vibration damping device, a casing,'a pair of spaced plates, a mem ber adaptedto oscillate between the plates, viscous matter in said casing to impede the oscillations of said member and fluid means cooperating with one of said plates to prevent variationsin the 'eifectiveness of said device. I I I i Inwitness. whereof, 'I hereunto subscribe my name this 21stdafi of Au st, 1928.

' CHARL S F. VIEBUSCI-I- damping device a casing 

